The invention relates to a device for transmitting an excursion of an actuator and a method for its production according to the independent Claims.
Actuators based on the piezoelectric principle are suitable for the highly precise and very rapid regulation of control processes, as are expedient for example for the activation of injection devices or valves in internal combustion engines. In order to achieve larger linear excursions of the piezoactuators, these have to comprise a number of individual piezoelements stacked one on top of the other. This has the disadvantage that the size of the structure assumes dimensions that are not permissible for many intended uses. For example the space for incorporating injection valves in the cylinder head of an internal combustion engine is limited so that there is generally no room for piezoactuators with the longitudinal dimension required for the required control motions. Smaller piezoactuators are therefore used, the linear excursions of which are translated by means of suitable lever devices into larger control member excursions.
An injection valve is known from U.S. Pat. No. 4,101,076 comprising a piezoelectric actuator, which activates an injection needle directly via a mechanical transmission element. The transmission element has two lever arms of different lengths, disposed at right angles to each other and connected to each other in a bearing area. The shorter lever arm is assigned to the piezoelectric actuator and the longer lever is assigned to the injection needle. The transmission element rests on the housing of the injection valve in the bearing area The excursion of the piezoelectric actuator is converted by the different lengths of the two lever arms into a larger excursion of the injection needle.
However the form of the transmission element offers only moderate rigidity, which results in imprecise excursion transmission in particular with highly dynamic circuit processes.
An injection valve is also known from WO 99/17014, with which mechanical transmission elements are provided for the transmission and translation of an excursion of a piezoactuator to a control member, said transmission elements essentially having the form of a cylinder, the limiting surfaces of which are configured in an essentially triangular manner, with the corners rounded. The width of the transmission elements causes planar bearing areas to be formed so that friction during transmission is reduced.
The object of the present invention is to provide a device for transmitting an excursion of an actuator, which is simple and small in structure and allows transmission and translation of actuator excursion to a control member with the lowest possible level of friction.
According to the invention, the device for transmitting an excursion of an actuator comprises at least one transmission element having a first, a second and a third bearing area, wherein the first bearing area is assigned to a counter bearing, the second bearing area is assigned to the actuator and the third bearing area is assigned to a control member. According to the invention, the at least one transmission element is supported with the first bearing area against the counter bearing when the actuator is operated and said transmission element moves the control member with the third bearing area by means of a rotational motion about a point of rotation, with the at least one transmission element being configured essentially in the form of a plate, which is disposed substantially perpendicular to the control motion and with the first, second and third bearing areas each being configured in the form of substantially straight surfaces on the plate.
The device according to the invention in particular has the advantage of minimizing the relative motion between the transmission elements, so that direct transmission of the excursions of the actuator is ensured with little wear and loss.
A distance between a central axis of the actuator and a central axis of the control member may be provided, with which the advantage of a relatively compact structure of the transmission element is associated, said transmission element being disposed between the actuator and the control member.
At least two transmission elements can be disposed opposite each other, which has the advantage of symmetrical distribution of the control forces both at the actuator and at the control member. Also with two transmission elements the control forces acting on each of these transmission elements are halved, as are the compressive loads acting at the respective bearing areas.
At least three transmission elements can be provided, which are disposed essentially concentrically in respect of each other. This has the advantage of further reducing the control forces and therefore the compressive loads at the respective bearing areas. Also with three or more transmission elements, these can be relatively compact in design, as they have to transmit less force in total.
Concentric central axes of the actuator and the control member can be provided, which has the advantage that the entire device is very compact. A fuel injector with the control device according to the invention can thus be relatively slim in design and is therefore also suitable for incorporation in very restricted spatial conditions, e.g. in the cylinder head of an internal combustion engine.
The plate of the at least one transmission element can be configured in a stepped manner. This embodiment according to the invention has the advantage of an ideally compact structural design, as it means that the distance between the actuator and the control member can be very small.
The second bearing area can be assigned to an upper side and the third bearing area can be assigned to a lower side of a first straight section of the stepped plate, which has the particular advantage of a very compact transmission element.
The second straight section of the stepped plate may partially encompass a lower sleeve area of the actuator, which also has the advantage of a very compact transmission element structure.
The plate can be produced by cold or hot forming. This has the particular advantage of favorable fiber orientation in the plate and therefore a very high level of strength in respect of plastic deformation subject to the operational loads occurring.
Ground surfaces of the bearing areas of the plate can be provided, with the advantage of minimizing friction between the surfaces of the bearing areas in contact.
An intermediate member connected to the actuator can be provided between the actuator and the second bearing area of the at least one transmission element. This embodiment has the advantage of an intermediate member which can be easily adapted to spatial conditions, thus contributing overall to a compact structure of the device according to the invention.
A positive, non-positive or material-fit connection between the actuator and intermediate member can be provided, which has the advantage that no further connection elements are required. This results in a light weight and a compact structure.
A linear contact between the raised edge of the intermediate member and the second bearing area of the plate can be provided, which has the advantage of good distribution of the forces occurring. Compared with point bearing, linear contact has the advantage of significantly lower compressive loads.
The height of the raised edge can be approximately 200 xcexcm. This ensures that a defined bearing line remains even in unfavorable conditions, which is not subject to such elastic or plastic deformation that the defined bearing line becomes an undefined bearing area.
The raised edge can be rounded, which has the advantage of continued linear contact even with angular motions.
Alternatively, the second bearing area of the at least one plate may have at least one raised edge, which is in contact with the intermediate member. This ensures that a defined bearing line remains even in unfavorable conditions, which is not subject to such elastic or plastic deformation that the defined bearing line becomes an undefined bearing area.
Ground surfaces of the intermediate member and/or the support element may be provided, which has the advantage of minimizing friction between the bearing areas.
The actuator can be a piezoelectric actuator, which has the advantage of very rapid longitudinal motion when relatively large forces have to be transmitted and very compact spatial dimensions.
A translation ratio in the range of approximately 1:4 to 1:20 can be provided for an excursion of the actuator to an excursion of the control member. This has the advantage that relatively large control motions can be executed with an extremely compact actuator.
Also, a translation ratio of approximately 1:6 between the excursions of the actuator and the control member can be provided, with the advantage that even when relatively large control motions have to be transmitted, sufficiently large forces can still be transmitted.
A device advantageously may comprise one or more of the above-mentioned features, for transmitting an excursion of an actuator, in particular a piezoactuator of an injection valve, in which at least a first lever device and a second lever device are provided, with the excursion of the actuator being transmitted from the first lever device to the second lever device. Two lever devices are thus xe2x80x9cconnected in seriesxe2x80x9d, as a result of which high lever ratios and therefore large control motions are achieved with an extremely compact structure. In certain cases intermediate parts or elements can be provided between the actuator and the first lever device and/or between the first lever device and the second lever device, if this is advantageous.
The excursion of the actuator can be transmitted from the second lever device to a control member. One or more intermediate parts or elements can thereby also be provided between the second lever device and the control member, if this is advantageous.
Even with embodiments with at least two lever devices, the first lever device and/or the second lever device can comprise at least one transmission element disposed substantially perpendicular to the direction of excursion of the actuator. This allows it to be ensured in a simple manner that the force transmitted to the control member is parallel to the direction of excursion of the actuator, as is often required.
In this context, according to preferred embodiments of the device, at least one transmission element can be essentially plate-shaped. A plate-shaped transmission element structure can effectively contribute to a compact structure of the device according to the invention.
According to one preferred embodiment of the device, at least one surface of at least one transmission element may be convex. An at least slightly convex form of the transmission elements can advantageously provide the necessary space for the relative motion of the transmission elements in respect of each other and/or of the transmission elements and the housing. Also an at least slightly convex form impacts advantageously on friction conditions, in particular when the relative motion is achieved as a result of sliding.
The device may comprise a first transmission element with a first, second and third bearing area and a second transmission element with a fourth, fifth and sixth bearing area, with the first bearing area being assigned to a first counter bearing, the second bearing area being assigned to the actuator, the third bearing area being assigned to the second transmission element, the fourth bearing area being assigned to a second counter bearing, the fifth bearing area being assigned to the first transmission element and the sixth bearing area being assigned to a control member. In some circumstances further elements can also be provided between the respective bearing areas and the components assigned to them, if this is advantageous.
In this context, provision is preferably also made for the first transmission element to be supported with the first bearing area against the first counter bearing when the actuator acts on the second bearing area and to act by means of a rotational motion with the third bearing area on the fifth bearing area of the second transmission element, said element being supported with the fourth bearing area on the second counter bearing and acting by means of a rotational motion with the sixth bearing area on the control member. Depending on the embodiment, translatory motions can in some circumstances be superimposed on the rotational motions of the transmission elements.
According to a particularly preferred embodiment of the device, one actuator central axis and one control member central axis may pass through the second bearing area and the sixth bearing area. This solution allows a particularly compact structure of the device according to the invention.
According to all the embodiments of the device, at least one counter bearing and/or at least one transmission element in the area of the first or fourth bearing area can have at least one rounded section, which allows rolling in respect of a relative motion between a housing and the transmission element. If a transmission element also executes a translatory motion in respect of the housing, this can in some circumstances be superimposed on the rolling motion. Rolling generally causes less loss than for example pure sliding and is therefore advantageous. Rolling also has a positive impact on wear.
In this context provision can also be made for at least one rounded section to be formed by at least one separate element. In this case it is preferable for surfaces of the housing and/or the transmission element(s) coming into contact with the separate element(s) to be adapted at least partially to the form of the separate elements.
According to another advantageous embodiment, at least one separate element can be supported in a rotatable manner in the housing.
Additionally or alternatively provision can be made for at least one separate element to be supported in a movable manner in the housing. In this case the at least one separate element can for example comprise a planar lower side, with which it can be moved on a housing section, and an upper side with a semi-circular cross-section, which forms the rounded section and allows the rolling of the transmission element.
With a particularly preferred embodiment, provision is made in this context for at least one separate element to be formed by a sphere or a drum. In this way for example embodiments can be produced, in which the transmission elements execute pure rotational or swinging motions in respect of the housing. In this case there is generally a greater relative motion between the respective transmission element and the component acting on it, whereby this relative motion can be achieved by sliding.
A method for producing a transmission element for a device according to the embodiments disclosed above comprises that the transmission element is forged and/or milled and then at least its bearing areas are ground. This method according to the invention has the advantage that it can be used to produce a transmission element according to the invention very economically. Also the transmission element is able to transmit large control forces over a long operating period. The method for producing an actuator according to the invention also has the advantage of a high level of precision for the production of identical transmission elements, which maintain their positive characteristics with a high level of constancy due to the low level of wear, even during long-term operation.
The device disclosed above is particularly suitable for an injection device. It is quite particularly suitable for an injection device which operates according to what is known as the pump-nozzle principle.